1. Field of the Invention
The present invention relates to a process for the production of cation-exchanged adsorbents. More particularly, the present invention relates to a single-step continuous ion exchange process for the production of cation-exchanged zeolite adsorbents.
2. Description of Related Art
Many techniques are known for making mixed-cation zeolites, such as calcium-lithium zeolites, by ion-exchange of existing sodium and/or potassium zeolites. At present, the processes for producing mixed cation zeolites require a complex and expensive sequence of successive ion-exchange steps in which ions present in the "raw" (i.e. untreated) zeolite are exchanged with other ions to produce a mixed cation zeolite product with the desired adsorbent properties. The prior art utilizes two basic methods for producing ion exchange materials containing mixed cations.
In a first method, the batches of raw (untreated) zeolite are exchanged with an aqueous solution containing the 35 ions which are to be introduced into the product zeolite. The ion composition of the aqueous solution, which is referred to in the art as "brine", is adjusted to be in equilibrium with the ion concentration desired in the mixed-cation zeolite product.
In a second method, the slow and inefficient batch exchange steps are replaced with fast and continuous counterflow steps in which untreated zeolite is continuously countercurrently exchanged with a brine containing the mixed cations to be introduced into the product zeolite. The ion composition of the brine is again in equilibrium with the ion concentration desired in the mixed-cation zeolite product.
The prior art methods either require a multi-step procedure which utilizes extra equipment and is time consuming, or require large amounts of brine which wastes valuable cations. The prior art methods are illustrated in Chao U.S. Pat. No. 5,174,979 and Milton U.S. Pat No. 2,882,244.